I. Field
Example aspects of the present invention generally relate to telecommunications, and more particularly to a system architecture for broadcast spectrum-sharing.
II. Related Art
Since the beginning of broadcasting, the television (TV) broadcast spectrum has operated mostly under the same network topology. According to this topology, a single transmission antenna is used to radiate a high power signal toward the radio horizon to cover receivers within a predetermined coverage area. Roof mounted aerial antennas are used to receive the signals. FIG. 1 shows an example of such a broadcast topology 100.
As shown in FIG. 1, a single, relatively tall transmission tower 110 is fitted with a high power antenna having a vertical pattern signal which is tilted downward slightly. The slight vertical beam tilt directs the RF energy outwards (coverage contour 140), toward the radio horizon 120, over a relatively large coverage area 160. TV receivers with roof mounted antennas many miles from the transmission tower 110 are able to receive these broadcast signals.
Unavoidably, however, the signal continues to propagate outwards for approximately three times (3×) the coverage contour distance (X). This has the effect of creating an interference contour 150. As a result, TV channels on the same frequency (co-channels) must be placed at large geographic distances apart to prevent co-channel interference among stations in adjacent market areas. The channels are thus rendered unusable over an occupied region which includes the interference contour 150. Accordingly, by design, a large portion of the spectrum in a region must remain unused to mitigate co-channel interference. To deal with the constraints of this topology 100 regulatory rules and channel allocation methodologies have been enforced.
FIG. 2A illustrates two adjacent transmission channels, channel A (210A) and channel B (210B) serving the same market. As shown in FIG. 2A, the coverage contours 240A, 240B overlap, which can cause adjacent interference. Receiver 220 receives a strong signal from transmission channel B (210B), while attempting, typically with difficulty, to receive a weak signal from transmission channel A (210A).
FIG. 2B illustrates two co-channel transmission channels which are located further apart than the transmission channels illustrated in FIG. 2A. While the coverage contours 240A and 240B do not overlap, their respective interference contours 250A, 250B do. The relatively large distance between co-channels 225A and 225B prevents co-channel interference, but the use of the spectrum is still inefficient. The “white space” 230 is essentially unusable.
A typical broadcaster business focuses on using the above-described high power/high tower broadcast (point-to-multipoint) infrastructure to distribute content to the public over a broad area of coverage. Local television stations, for example, produce and distribute content such as news, weather, sports, traffic, community events/services, emergency information, etc., to their television market.
A typical 3GPP LTE Mobile Network Operator (MNO) focuses on optimizing its systems primarily for unicast (point-to-point) modes, with a primary design constraint being low latency. This permits latency-dependent applications such as voice over internet protocol (VoIP) and gaming to be best served.
3GPP Long Term Evolution (LTE) is a standard for wireless communication of high-speed data. One feature of LTE is called Multicast Broadcast Signal Frequency Network (MBSFN). MBSFN is capable of delivering broadcast (point-to-multipoint) and unicast (points-to-point) IP multimedia services using the LTE infrastructure.